SEM/EDS analysis of soil and roasting vessels fragments from ancient mercury ore roasting sites at Idrija area

Abstract

Numerous roasting vessels fragments can be found at ancient roasting site areas in the surroundings of Idrija town, which were used for ore roasting in the first 150 years of Hg production in Idrija. The earthen vessels fragments lay just below the surface humus layer and in some parts they stretch more than 1 meter deep; they are covered with red (cinnabar) or black (metacinnabar) coatings. SEM/EDS analysis of roasting vessels fragments and soil samples from roasting site areas Pšenk and Frbejžene trate was performed in order to characterize the solid forms of Hg in applied sampling material. Mercuric sulphide HgS was found to be the main mercury compound present in the samples. Analysis of earthen vessels fragments showed abundant HgS coatings on the surface of ceramics, forming either crust-like aggregates on matrix or isolated grains. Some well-shaped grains with indicated structure and the size of up to 200 (μm could also be observed. In soil HgS was present as powder-like concentrations scattered in soil samples, frequently coating silicate and quartz crystals and clay-minerals. Polycristalline, mercury- and sulphur- rich particles comprising silica, clay minerals and AI-, Fe- and Mg-oxides that were also observed in the samples were interpreted as soil aggregates infiltrated by mercuric and sulphur vapours and by liquid mercury spilled during roasting. These particles suggest a possible presence of mercury-sulphur associations other than HgS.